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Growing Your Own Growing Your Own Vegetables | Composting | Container Gardens | Fall/Winter Gardens | Fertilizing | Insect Pests | Plant Diseases | Planting Guidelines | Raised Beds | Regional Tips | Site Selection | Slugs | Soil Improvement | Tilling | Warm-season Crops | Watering | Weeds Improving Garden Soil  Types of amendments  How to use amendments  How much amendment to add?  Cover crops Making a poor garden better often begins with the soil. If your garden soil is poor, consider giving it some help. Adding organic materials to sandy soils improves their nutrient- and water-holding capacity. Adding organic materials to clay soil improves drainage and aeration, and helps the soil dry out and warm up more quickly in the spring. Types of amendments Good organic amendments (additions) for garden soils include wood by-products such as sawdust and bark mulch, peat moss, rotted manure, grass or wheat straw, and compost. Inorganic amendments include pumice, perlite, vermiculite, and sand. Any composted material that has been reduced to humus is a good soil amendment. For example, rotted manure is an excellent soil amendment if it has been properly composted to kill weed seeds. Unfortunately, many manures contain a lot of uncomposted bedding materials such as sawdust, wood chips, or straw. These organic materials are high in carbon content and low in nitrogen and will inhibit plant growth unless you add extra nitrogen. Microorganisms in carbon-rich amendments take free nitrate nitrogen out of the soil to build their own tissues. Therefore, less nitrogen is available for plants until the excess carbon-rich organic matter breaks down. The breakdown of organic matter high in carbon content would take years with the nitrogen naturally present in cattle or horse manure. To speed up the process, mix additional nitrogen into your garden-at least 6 pounds of ammonium nitrate or 10 pounds of ammonium sulfate per inch of organic matter applied over a 1,000-square foot area. Peat moss, with its high humus content, is the ideal amendment for raised beds or small gardens because it is nearly weed-free. However, it is expensive to use in large gardens. Inorganic amendments such as perlite, sand, and vermiculite don't contain humus or contribute to its production. Inorganics function primarily as wedges that separate soil particles, increasing soil porosity and aeration. Sand is low in both water- and nutrient-holding capacity and causes finer silt or clay soils to compact. Mix sand with an organic amendment such as peat moss or sawdust to improve the sand's amending properties. How to use soil amendments Thoroughly rototill any amendment into garden soil to prevent layering. Rototilling organic amendments into gardens in the fall gives soil microorganisms an early start on converting organic matter to humus. Another rototilling in spring will thoroughly mix in the amendments. (See story on tilling.) How much amendment to add? To make a significant change in your garden soil, an amendment must equal at least one-third of the volume of the soil you are amending. For example, to amend a garden to a depth of 1 foot, you need to add one-third of a foot (4 inches) of material. How much volume of material is this? Here's how to figure out (using a 20-foot x 50-foot garden as an example): Multiply width x length to get area: 20 feet x 50 feet = 1,000 square feet Multiply area x 0.333 (one-third of a foot) to get cubic feet: 1,000 square feet x 0.333 = 333 cubic feet Divide cubic feet by 27 to get cubic yards: 333 cubic feet ÷ 27 = 12.33 (1213) cubic yards Cover crops such as crimson clover protect garden soil from winter rain and add organic matter when tilled in. Cover Crops One way to amend garden soils that requires minimum effort is to plant a green manure cover crop. An excellent winter cover crop for western Oregon is crimson clover. Plant 12 pound of seed per 1,000 square feet. Plant no later than October 1 and water the bed so the crop is established before cold weather sets in. When rototilled under in late April, crimson clover will produce 3 to 4 pounds of nitrogen per 1,000 square feet. Fava beans or Austrian winter peas make an excellent spring cover crop for tilling under in the summer. Plant in early April at a rate of 12 pound of seed per 1,000 square feet. Rototill the crop when it begins to bloom. Rototill green manure crops at least 2 weeks before planting your garden. A final pass with the rototiller just before you plant usually is sufficient to prepare garden soil for seeding vegetables. Never rototill wet soil or you'll cause heavy clodding in the soil and a compacted "tiller pan" beneath the rototilled layer. A good seedbed contains loose, friable soil that is free of compacted lumps. (See story on tilling.)

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